In consumer electronics, power consumption is becoming an increasingly important design consideration. For example, with regard to television (TV) power supplies, of particular focus is the power consumption of the device during standby mode, i.e., when the device is powered down and awaiting an activation signal. Efficiency standards, such as the Energy Star® standard, require very minimal power consumption (e.g., less than or equal to 270 mW) during standby mode. Efficiency standards also typically contain power factor correction requirements so that reactive power is not wasted in the system through reflection of higher order harmonics. For example, the Energy Star® standard specifies the maximum amplitude of line-frequency harmonics up to an including the 39th harmonic.
Power supplies for consumer electronics are typically required to deliver to power to various loads within the device. In many cases, these loads may have different power requirements and may require independent power sources. For this reason, consumer electronics typically include multiple power supplies. In addition, consumer electronics typically include power factor correction circuits to bring the load current in phase with the load voltage and consequently increase the power factor of the circuit.
In a device with multiple power supplies, it can be very difficult to meet standby power mode requirements by using one of the power supplies and its associated control circuitry. One solution is to provide a dedicated auxiliary mode power supply in the device that meets efficiency requirements and delivers all of the necessary power during the auxiliary power mode. However, this solution introduces additional component cost into the device. Furthermore, this solution requires additional area for the auxiliary power supply and thus limits the overall size of the device.